Peguero, G., Bonal, R., Sol, D., Muñoz, A., Sork, V.L., Espelta, J.M. (2017) Tropical insect diversity: Evidence of greater host specialization in seed-feeding weevils. Ecology. : 0-0.EnllaçDoi: 10.1002/ecy.1910
Fernandez-Martinez M., Garbulsky M., Penuelas J., Peguero G., Espelta J.M. (2015) Temporal trends in the enhanced vegetation index and spring weather predict seed production in Mediterranean oaks. Plant Ecology. 216: 1061-1072.EnllaçDoi: 10.1007/s11258-015-0489-1
The extremely year-to-year variable production of seeds (masting) is an extended plant reproductive behaviour important for forest dynamics and food webs. The dependence of these episodes of massive seed production on recently or long-term photosynthesised carbohydrates, however, remains controversial. In this paper, we explore whether vegetation (tree canopy) changes, detected using EVI as a proxy of leaf area and photosynthetic capacity, can provide a reliable estimation of seed production. To complete this analysis, we also explored the effect of weather both in the trends of EVI and in acorn crop size. To this end, we compared the trends of the EVI and acorn production over 10 years (2000–2009) in five stands of Quercus ilex L. in Barcelona (Catalonia, NE Spain). We found that acorn production was mainly driven by a combination of: (i) a minimum initial threshold in the EVI values, (ii) an increase in EVI in the 9 ± 4 months prior to reproduction, and (iii) appropriate weather conditions (low water stress) during spring. These results indicated, apparently for the first time, that reproduction in masting species could be detected and partly predicted by remotely sensed vegetative indices. Our results suggested that this particular reproductive behaviour in Mediterranean oaks was driven by a combination of two factors, i.e. good and improving vegetation conditions, as shown by a minimum initial threshold and the increase in EVI needed for large seed crops, and the need of wet weather conditions during spring. Moreover, our results fully supported recent studies that have associated short-term photosynthate production with seed production. © 2015, Springer Science+Business Media Dordrecht.
Peguero G., Bonal R., Espelta J.M. (2014) Variation of predator satiation and seed abortion as seed defense mechanisms across an altitudinal range. Basic and Applied Ecology. 15: 269-276.EnllaçDoi: 10.1016/j.baae.2014.03.006
Predator satiation and seed abortion have been reported as effective mechanisms reducing pre-dispersal seed predation, however, whether they may act simultaneously and whether their contribution to seed defense may spatially vary has been barely addressed. Across the altitudinal range of the dry tropical tree Acacia pennatula we investigated the importance of seed production and seed abortion as defense mechanisms against its pre-dispersal seed predators (Mimosestes spp.). Additionally, we measured the potential relationship between the number of seeds that escaped predation and plant recruitment. Predator satiation was effective since greater fruit production was associated with a lower proportion of predated seeds, while high seed abortion rates were related to increases in larval mortality. Although both mechanisms were present simultaneously, their relative contribution varied considerably across the altitudinal range: predator satiation was favored in the middle parts of the range, where seed production is much higher, whereas seed abortion was particularly relevant at the peripheral sites and especially high at the upper margin. The number of seeds that escaped predation was related to seedling density at plot level, indicating the demographic significance of these defense mechanisms against pre-dispersal seed predation. Overall, these results highlight the importance of considering spatial variability when analyzing seed defense traits and they also suggest considering predator satiation and seed abortion as two complementary mechanisms to reduce seed loss. © 2014 Gesellschaft für Ökologie.
Peguero G., Espelta J.M. (2014) Endozoochory and Fire as Germination Triggers in Neotropical Dry Forests: An Experimental Test. Biotropica. 46: 83-89.EnllaçDoi: 10.1111/btp.12076
Endozoochory and fire are crucial ecological factors determining germination success and recruitment in many plant species. Fire is a well-known germination trigger while endozoochory may allow seed dispersal along with an increase in germination. Their interaction has rarely been addressed, however, even though both factors are pervasive in human-transformed ecosystems like most Neotropical Dry Forests (NDF). For three common Mesoamerican tree species (Acacia pennatula, Enterolobium cyclocarpum, and Guazuma ulmifolia), we used feeding trials to assess the preference of cattle, which are their main seed dispersal agent. We also experimentally tested the interaction between gut passage and fire as triggers of germination. The fruits of the three species were eaten by cattle, but the small seeds of G. ulmifolia were ingested 10-fold more than those of the other species. While gut passage did not have any effect on germination, heat-shocks above 90 °C increased the number of germinating seeds by 15 percent. These results suggest that cattle may be a key dispersal vector in NDF, but that fire may be an important germination trigger. Physical dormancy in these species may have been selected for by extinct megaherbivores because it was a key trait ensuring seed survival after gut passage. However, in light of the recent expansion of cattle-ranching and fire occurrence in NDF, it has become a useful exaptation facilitating the colonization of disturbed areas. © 2013 The Association for Tropical Biology and Conservation.
Peguero G., Espelta J.M. (2013) Evidence for insect seed predator dynamics mediated by vertebrate frugivores. Revista Chilena de Historia Natural. 86: 161-167.EnllaçDoi: 10.4067/S0716-078X2013000200005
Vertebrate frugivores have been suggested to reduce seed predation, indirectly controlling populations of insect seed predators (ISP) by means of consuming many individuals when feeding on fruits. The possibility has not been explored, however, that this 'frugivore predation' may differentially affect ISP according to species-specific differences in larval development time within the fruit. In the dry tropical forest trees Acacia pennatula and Guazuma ulmifolia we compared seed predation and the absolute and relative abundances of bruchid beetle species (Bruchinae) in two sites, one with large frugivores (cattle) and the other cattle-free for a considerable time. In the site with cattle we found a notable overall reduction in the proportion of seeds predated (ca. 15 %) with respect to cattle-free site, and changes in the ISP community as well, in particular a reduced absolute and relative abundance of the bruchid species with the longest larval development time. Our results suggest that the interplay between evolutionary processes (resulting in variation in insect life-histories) and complex ecological interactions (inadvertent consumption by larger animals) may contribute to the coexistence of different insect species feeding upon the same host plant. © Sociedad de Biología de Chile.
Peguero G., Lanuza O.R., Savé R., Espelta J.M. (2013) Allelopathic potential of the neotropical dry-forest tree Acacia pennatula Benth.: Inhibition of seedling establishment exceeds facilitation under tree canopies. Plant Ecology. 213: 1945-1953.EnllaçDoi: 10.1007/s11258-011-0014-0
Secondary succession after land abandonment in tropical dry forests has been suggested to be favoured by the facilitation effects for seedling establishment exerted by pioneer trees isolated in these savannah-like landscapes. However, it has also been noticed that these pioneer species may sometimes have an encroaching effect and arrest succession for several decades. We investigated in this study whether allelopathy can play a role in limiting seedling establishment of co-occurring tree species under the canopy of Acacia pennatula by means of lab bioassays and field experiments in north-west Nicaragua. Leaf extracts of A. pennatula did not affect seed germination but reduced the general growth and especially the development of the root compartment in seedlings, shifting their biomass allocation model to a reduced root/shoot ratio. Survival of planted seedlings under the canopy of A. pennatula was about 20-30% lower than outside, and this reduction was particularly pronounced as the dry season progressed, despite the milder conditions (e. g. higher soil moisture) being experienced in the inner positions under the canopy. Altogether, our results suggest that, rather than facilitating, A. pennatula may inhibit the establishment of seedlings under its canopy probably by means of an allelopathic interference in the development of the root system with critical negative consequences for young seedlings in terms of overcoming the dry season. This article warns about overemphasizing the nucleation effect that remnant and isolated trees may have to facilitate secondary succession in these highly disturbed savannah-like tropical dry forests. © 2011 Springer Science+Business Media B.V.
Peguero G., Espelta J.M. (2011) Disturbance intensity and seasonality affect the resprouting ability of the neotropical dry-forest tree Acacia pennatula: Do resources stored below-ground matter?. Journal of Tropical Ecology. 27: 539-546.EnllaçDoi: 10.1017/S0266467411000290
Many plant species in tropical dry forests partly base their ability to persist after disturbance on resprouting. Yet little is known if this ability can be affected by the intensity and seasonality of disturbance and whether the amount of resources (starch, N, P) stored in the taproot may constrain this response. We investigated resprouting after experimental clipping or burning, applied before or after the dry season and repeatedly in Acacia pennatula individuals in wooded rangelands of North-West Nicaragua. Each treatment was applied to 12 trees and replicated in six plots. One year after the onset of the experiment, survival and biomass recovery were significantly lower in burned than in clipped individuals (78% ± 4% and 75.3 ± 8.0 g vs. 94% ± 2% and 79.1 ± 6.8 g; mean ± SE). Whatever the disturbance applied, trees disturbed after the dry season significantly showed the lowest survival, growth and concentration of N and P. These results suggest that resprouting in dry tropical species may be constrained by intense disturbances (e.g. burning) but especially if they occur towards the end of the dry season. This phenological constraint could be due to the reduced availability of N and P as this dry season progresses. © 2011 Cambridge University Press.
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